For the second time this year, government auditors have issued a report critical of the Obama administration’s projections for preserving the nation’s stockpile of nuclear weapons.

In both instances, the cost estimates put forth by the departments of Defense and Energy have been described as far too low, in part because key expenses were not budgeted. The latest audit, performed by the Government Accountability Office (GAO), supported some of the findings of the Congressional Budget Office (CBO), which concluded six months ago that the administration was off—by hundreds of billions of dollars—in estimating the future needs of maintaining the arsenal.

The Pentagon has claimed outlays will be about $264 billion. But the CBO put the figure closer to $570 billion and perhaps as much as $1 trillion over the next 30 years.

The GAO did not offer its own estimate for maintaining the weapons. But it did question the Defense Department’s claim that modernizing all ballistic missiles and bombers would require only $64 billion over the next 10 years.

In the case of the Minuteman III missile, which has served as the backbone of the nation’s land-based nuclear deterrent since the 1970s, GAO auditors found the administration left out all future funding for replacing these weapons, saying the program was “not yet defined.” As for a new bomber, the Air Force said those costs were “too sensitive” to include in the report.

At the Energy Department (DOE), which oversees all nuclear weapons research, the GAO found that officials had low-balled the cost of modernizing certain warheads for ballistic and cruise missiles.

The agency also reported that DOE had assumed billions of dollars in cost savings from efficiency efforts without determining where the savings would come from, and that Energy officials had left out the cost of revamping or replacing several nuclear-weapons laboratories.